[bestgenman]

Those indicators are neon rated at 125VAC, when they age the firing of the gas diminishes.  (there are wiser folks on here who can explain the physics better than I).  These lamps are fed from the fuses on the transfer switch, one lamp for each source (shore & generator).  But, only one leg of each source from the XFER.  I suspect the other leg is tied to your voltmeter.  I'm not completely clear on the wiring and am drawing conclusions based on your description.  As you say your voltmeter isn't working now so i suspect the fuse for the voltmeter is blown.  They are located inside the AC distribution panel and rated somewhere around 2 to 4 amps.  Not wise to use anything larger for either fuse.

I hope this helps.  I bet there is someone on the site who has thoroughly dissected the meter wiring and may provide a clearer picture.